Getter devices are well known in the art and are used for a variety of reasons. One use is to produce and maintain the vaccum in electrical discharge vessels thus reducing the manufacturing time required to produce said vessels and also increasing their effective working life. Getter devices can also be used within gas or vapor filled electrical discharge vessels such as numerical indicator tubes or fluorescent lamps where their main function is to reduce the presence of reactive gases. Getter devices are also used in a wide variety of other devices such as devices using particle beams (e.g. cathode ray tubes), gas purifiers and nuclear fuel elements.
Getter materials are usually divided into two main groups. Getter materials of the first group are called "flash" or "evaporating" getter materials. These getter materials derive their name from the fact that the getter material is evaporated from its container by quick heating, or flashing. The getter material is then dispersed onto a suitable surface.
In order to place the getter device within the vessel, in the case of non-evaporating getter materials, it is known to paint the getter material in the form of a fine powder held in a binder directly onto one of the components within the vessel such as the anode or the electrode supports. The component is then heated under vacuum whereupon the powdered getter material sinters to the component and the binder evaporates away. However the presence of such a getter material on the functioning parts of the electrical discharge device or other vessels may have a deleterious effect on the efficient operation of such devices. Also their functioning parts may be so delicate that it is not possible to support the getter material on said parts. Frequently it is more economical for the manufacturer of the electrical discharge or other vessel to insert an already fabricated getter device into said vessels rather than make his own getter device within or on the surfaces of said vessels. For these and other reasons it is desirable to produce separate getter devices of both groups which can be used later within a whole variety of electrical discharge or other vessels.
Many attempts have been made to produce suitable getter devices having desired characteristics. In U.S. Pat. No. 2,082,268 active getter material is deposited upon a loosely packed porous structure for example of glass wool, however, the getter device is complex and difficult to manufacture. Moreover, it is very heavy in relation to the amount of getter material contained. U.S. Pat. No. 3,102,633 uses a particulate support of graphite in chemical combination with an alkali metal. Della Porta in U.S. Pat. No. 2,824,640 proposed the use of a ring shaped channel support of "U" section containing an evaporating getter material. However several disadvantages were found, such as low percentage getter metal yields and the production of loose particles or even disintegration of the getter mass when large barium quantities are required to be evaporated. In an attempt to overcome these difficulties, Reash in U.S. Pat. No. 3,428,168 proposes the use of a wire or "L" shaped anchoring element within the support whereas della Porta in U.S. Pat. No. 3,385,420 proposes an increase in the free surface area of the evaporating getter material by removing as much of the support as possible, but increasing the risk of producing loose particles from unsupported edges.
Non-evaporating getter devices have also been used by containing the active getter material in a "U" section ring container and as tablet shaped forms supported upon a wire gauze, see della Porta U.S. Pat. No. 3,225,910. Unfortunately their manufacture involves the use of high compression forces which reduces the porosity of the getter mass and hence reduces its gettering properties. Wire heating coils have also been used to support non-evaporating getter devices (see U.S. Pat. No. 3,584,253), but it is difficult to apply the getter material to the coil in reproducible quantities, and the application process is very lengthy.
Other vapor generating devices contained within a sintered mass of supporting material are described in U.S. Pat. No. 3,579,459. However, the sinterizing material forms at least 30% of the bulk of the vapor generating mixture and still has to be placed in a container. Furthermore, the sintering process is very lengthy, more than 1 hour, and may cause degradation of the other components of the mixture. Such sintered structures are characterized by relatively low porosity. Such sintered structures are also used as dispenser and impregnated cathodes where barium is allowed to diffuse slowly through, or is produced in the porous mass which is usually sintered titanium or molybdenum powder of about 17-27% porosity. Evaporation of barium is very low. Even though the cathode may sorb some gas it is not the required function, which is to produce electrons, and gas sorption is very inefficient. Further the production of these cathodes is very lengthy. Such dispenser and impregnated cathode structures are described in the following references: Revue Technique Philips, Vol. 11, No. 12, pages 349-358 and Revue Technique Philips, Vol. 19, No. 7-8, pages 230-244.
Accordingly it is an object of the present invention to provide an improved getter device which is substantially free from one or more disadvantages of the prior art.
A further object is to provide a getter device having minimum weight in relation to the weights of the getter material so supported.
Another object is to provide a getter device providing minimum obstruction to the desired action of the getter material.
Another object is to provide a getter device adapted to prevent the production of loose particles or disintegration of the getter mass by extending the support throughout the getter mass.
Yet another object is to provide a getter device having a large geometric surface area which defines a volume in which can be placed reproducible quantities of getter material.
A further object is to provide a getter device provided with an integral attachment means.
Another object is to provide a getter device whose attachment means provides minimum obstruction to the getter material.
Another object is to provide a getter device capable of being produced by mass production methods.
Another object is to provide a getter device capable of being attached to its working position as easily as possible and, if required, by automatic means.
Still another object is to provide an improved method for manufacturing a getter device.